Many commercially available vacuum cleaners combine suctioning and carpet fiber agitation to clean carpets. Brush rolls and beater bars are common means of agitating carpet fibers. The bristles or beater bars of brush rolls are used to agitate carpet fibers to loosen dirt to be removed by the suction of a vacuum producing fan. However, the use of brush rolls entails many disadvantages caused by the harshness with which they engage the carpet surface. In order to clean a carpet, it is only necessary to vibrate the fibers to loosen dirt and excessive pounding or grinding of the carpet fibers may be counterproductive in terms of both cleaning and carpet wear. For example, the rotating friction producing motion of brush roll bristles and the pounding motion of beater bars may actually push dirt deeper into the carpet where it cannot be removed by the vacuum. In addition, the pounding motion of the beater bar and the fiber pulling rotation of brush roll bristles wear the carpet. Some vacuum cleaners which incorporate brush rolls are not recommended for use on bare floors such as hardwood or linoleum because they may damage unprotected floors.
The use of brush rolls increases the cost of a sweeper. The brush roll is one of the most costly parts of a sweeper. In addition to their expense, brush rolls and their attending parts such as belts, bristle fiber and bearings tend to wear out before other components of the vacuum cleaner. The conventional use of brush rolls and beater bars increases the height of the motor housing of the sweeper. Because of their housing height most sweepers with brush rolls and beater bars can be moved only a limited distance under furniture.